1. Field of the Invention
This invention relates to an underwater foundation leveling device equipped with a plumb weight for leveling an underwater foundation and a unit that detects a position of a foundation area to which leveling is performed (hereinafter referred to as “leveling area”).
2. Description of the Related Art
An underwater foundation leveling device has been known, which drops a plumb weight 1 suspended from a crane onto a riprap in water to form a foundation footing in water. FIG. 6 shows an example of such an underwater foundation leveling device which includes a wire lock unit 3 which is secured to the upper end of a pipe-shaped support element 2 to the lower end of which a plumb weight 1 is secured. A wire rope (or chain) 4 secured to the lock unit 3 is coupled to a shipboard crane C and is wound and unwound to lift up and down the plumb weight 1. The foundation is leveled by act of the impact force generated by the fall of the plumb weight 1.
A position of a leveling area is detected in a process for leveling the bottom of a body of water so that a foundation with a target size and a target height is formed by falls of the plumb weight 1.
The use of a position measurement device for the positional detection of a leveling area is known from, for example, Japanese Patent 3225485. A position measurement device 7 comprises a plurality of reflectors 5 which are mounted along and on the outer periphery of an upper portion of the support element 2, a light receiving unit 6 which emitting a light beam a to the reflectors 5 and receives the reflected light a′, and a function of calculating a height and two-dimensional position coordinates of the reflectors 5 on the basis of the reflected light a′ received thereby.
If the position measurement device 7 determines the position of the reflectors 5 on the basis of the reflected light a′, the position of the plumb weight 1 can be determined by calculation based on the length of the support element 2. As a result, the position of the plumb weight on the bottom of a body of water is determined as a position of a leveling area on which the leveling work is being performed.
As described above, a plurality of reflectors 5 are disposed circumferentially on the outer periphery of the upper portion of the support element 2 in order to measure a position of a leveling area.
On the other hand, for allowing the plumb weight 1 to freely fall, the wire 4 coupled to the lock unit 3 is freely unwound from a reel (not shown) such that a smooth fall of the plumb weight 1 is not inhibited.
For this reason, when the plumb weight 1 hits the leveling area and stops, an extra-length portion of the wire 4 may be unwound through the inertia of the reel in some cases. If an extra-length portion of the wire 4 is unwounded in this manner, slack will occur in the wire 4.
Alternatively, the plumb weight 1 may possibly bound upon hit against the leveling area. In this event, slack will also occur in the wire 4.
It is close to impossible to eliminate such slack. As the amount of slack increases, the hanging wire 4 may possibly collide with the reflectors 5 as shown in FIG. 7. Since the wire 4 is used to hoist the support element 2 with the plumb weight 1, a high strength is required, so that a thick and robust wire is formed.
If such a wire 4 collides with the surface of the reflector 5, the reflector 5 could be damaged or the surface of the reflector 5 could be made dirty. If the reflector 5 is damaged or made dirty, it gives rise to disadvantages such as the reflector 5 is incapable of reflecting light, the direction of the reflected light is changed, or the amount of reflected light is decreased, resulting in incapability of correct position measurement.
it is an object of the present invention to provide an underwater foundation leveling device capable of inhibiting a collision of a wire with a reflector even when slack occurs in the wire locked to a support element to which a plumb weight is mounted.
In a first aspect of the present invention, an underwater foundation leveling device includes a support element mounted with a plumb weight used for leveling of a surface of riprap forming a foundation in water, and a plurality of reflectors provided around an upper portion of the support element for measurement of a position of a leveling area. The support element is hoisted with a wire and then made to fall by its own weight for leveling for the surface of the foundation. The reflectors reflect light back toward a light receiving unit for a detection of the position of the leveling area. The underwater foundation leveling device thus structured includes a protective element that prevent the wire in which slack occurs from hitting the reflectors, and a light passage located in a position allowing an optical path of the light reflected from the reflectors to travel toward the light receiving unit.
In a second aspect of the present invention, the protective element is provided above the reflectors, and the light passage is provided under the protective element. In addition, the protective element has an outer edge extending outward beyond a circle formed by the plurality of the reflectors continuously arranged adjacent to each other, and the outer edge is maintained in a relational position where, when the slack wire hits the outer edge, the wire does not collide with the reflectors.
In a third aspect of the present invention, based on the first aspect, the protective element is preferably formed in a dome shape.
In a fourth aspect of the present invention, based on the second aspect, the protective element may is preferably formed in a dome shape.
In a fifth aspect of the present invention, based on the first aspect, the protective element includes a pair of protective members respectively placed on upper and lower sides of the reflectors, and the light passage is provided between the pair of protective members. In addition, each of the protective members has an outer edge extending outward beyond a circle formed by the plurality of the reflectors continuously arranged adjacent to each other. The outer edge is maintained in a relational position where, when the slack wire hits the outer edge, the wire does not collide with the reflectors.
In a sixth aspect of the present invention, based on the first aspect, the protective element surrounds all the reflectors and the light passage is provided in the protective element.